The invention relates to the rapid cooling of moisture containing farinaceous foodstuff articles, such as bread, piecrusts and the like, using reduced pressure techniques.
The invention further relates to the production of a completely baked moisture-containing farinaceous foodstuff article, which makes use of a reduced pressure technique.
There are many instances in the food industry, where a foodstuff article is subjected to a heating process and it is then necessary to allow the article to cool before the next stage in handling it. Taking as a specific instance baked farinaceous foodstuffs, when those are removed from the oven, it is necessary to allow them to cool before processing such as wrapping, or, in the case of bread, slicing. Bread for example, may be at approximately 100.degree. C. in the crumb structure at the core when removed from the oven, but must be allowed to cool to below 30.degree. C. before slicing and wrapping. The cooling process is very time consuming - between two and three hours for ordinary bakers loaves - and also requires considerable storage space in the bakery for the product which is at the cooling stage. Besides the cooling process being time consuming, the apparatus required for cooling is bulky and expensive.
It will be appreciated that if the article at a given temperature is subjected to a reduced pressure, by which is meant a pressure lower than normal atmospheric pressure, the temperature of the article will exceed the boiling point of the moisture at that pressure, and there will be evaporation of moisture. The latent heat of evaporation is thus extracted from the article.
It has been proposed to cool bread by a two-stage process, which involves, first deliberately allowing the bread to cool in the conventional manner and then subjecting it to a vacuum. Clearly this would only partially improve the conventional process, because it still requires a relatively long pre-cooling period, before the vacuum treatment commences. Even more serious however is the fact that the prior proposal does not include any control over the application of the vacuum.
Obviously it is desirable to cool the article as quickly as possible, but if the pressure is reduced too rapidly, the moisture attempting to escape from the core of the article causes physical disintegration of the article. On the other hand, if the vacuum is applied at a slower rate, than in order to cope with the vapour emitted by the article, the reduced pressure treatment has to be prolonged, and with some products this creates a moisture denuded peripheral layer.
It has also been proposed to submit bread to a deliberate pre-cooling period after it has left the oven, to allow it to attain a temperature of about 135.degree. F. (58.degree. C.), and then to apply a two-stage vacuum treatment. This offers only a partial solution to the problem of time and space saving, because it is still necessary to leave the product for a considerable time - perhaps one hour - before the vacuum cooling can commence.
Although there may be some baked articles wherein the moisture can be allowed to escape as rapidly as possible, without detracting from the properties of the article, it will usually be found that the sudden application of a very low pressure would cause the article to disintegrate or explode. However, it must be appreciated that moisture is present in most baked farinaceous articles in two forms, namely molecular bound moisture - usually H.sub.2 O - which is chemically or physically combined with some other element(s) in the article and "free" moisture which is not chemically combined. The expression "molecular bound" is used in preference to "chemically combined" because to some extent the process of removing the moisture from the molecules is reversible. Now clearly if the reduced pressure treatment is carried to the point where some or all of the molecular bound moisture is released, the article will undergo a physical and/or chemical change, which will be deleterious, and will probably destroy it as a commercial article.
The problem which the present invention sets out to solve is to reduce the cooling time of baked moisture-containing farinaceous foodstuff articles without on the one hand disintegrating the article, and on the other hand creating a water-denuded boundary layer in the article.
It has also been found that the invention can be used to produce a completely baked moisture-containing farinaceous foodstuff article in a reduced time.